It has previously been proposed to provide a heating and/or air conditioning installation for a motor vehicle with a filter apparatus for filtering the air which is passed into the cabin of the vehicle, so as to remove contaminants, and in particular dust and smells. The specification of published European patent application No. 0 183 937 describes one filter apparatus of this kind, which includes a housing through which an air stream is arranged to pass, with two filter members pivotally mounted within the housing for movement between a working position, in which the air stream is forced to pass through the filter members, and a retracted position in which the air stream passes freely through the housing without passing through the filter members.
This known apparatus has a drawback, having regard to the fact that, when its mode is changed from the working position to the retracted position, contaminants which are carried by the filter members may be drawn into the cabin of the vehicle by the air stream. This disadvantage is also to be found in the filter apparatus described in the specification of German patent application No. 3 737 010.